I. Field
The present disclosure relates to an optical system and an imaging system.
II. Description of the Related Art
There is a need for optical elements which cut Infrared (hereinafter referred to as ‘IR’) in optical systems for imaging apparatuses such as general cameras. This is because IR included in components of sun light and so on affects an influence of image deterioration and so on to a captured image. For this reason, generally, an IR cut filter (hereinafter referred to as ‘IRCF’) is disposed in front of the image so that transmission of IR is inhibited.
Though it is possible to cut infrared by the IRCF such as described above, an occurrence of a ghost becomes a problem due to the IRCF. Also, as an IR cut coat (hereinafter referred to as ‘IRCC’) which cuts IR, there is a method for coating the IRCC to a lens surface of a lens between a foreground of an optical system and an image surface of an image sensor. But, there is a problem that a reflection property of the coat is changed by unevenness at a central part and a surrounding part of the lens surface in the case of coating the IRCC on a lens surface having curvature.
For reducing the occurrence of the ghost, a technology that the IRCC is coated on a side of an emission surface of a prism has been known. This technology has a good IR cut function and attempts to inhibit the occurrence of the ghost due to the IR cut structure. (Refer to Japanese Patent Application Unexamined Patent Application Publication No. 2006-017837). However, the technology discloses that the IRCC is coated on the prism surface which is on special optical elements. Therefore, there is a problem to attempt to fully inhibit the occurrence of the ghost.